In the field of audio, sound as close to original sound as possible has been pursued in respective components such as an amplifier, a speaker, a CD player, and a cable as audio devices. Even though a transition from an analog era to a digital era has been made, and various innovative technologies have been applied, technologies used in the process of recording to reproduction still have a limitation, and the current situation is that original sound cannot be reproduced as faithfully as the human sense of hearing perceives. One of the factors that prevent an audio device from pursuing original sound (e.g., sound of live music by an orchestra) is an influence of vibration on the audio device. As is well known, an audio device generates vibration by itself, and is externally influenced by various vibrations. In the case of an amplifier, “beats” due to an AC elementary signal of a power transformer and its harmonic components occur. In the case of a CD player, a motor that rotates a disk serves as a vibration source. In the case of a speaker, reaction force of a voice coil that drives a cone vibrates a speaker enclosure main body. This vibration is propagated to a floor surface where the speaker is placed, and excites complex natural vibration modes of the whole of a room including the floor surface. The disturbance vibration superimposed on the original sound in a complex manner again vibrates the speaker main body. A hypothesis that cross modulation distortion (sub-harmonics) generated at the time of the revibration deteriorates sound quality of the audio device has been proposed; however, the point that vibration due to mutual interference between the audio device and the placement surface is an important factor reducing quality of reproduced sound is considered to be an accurate fact.
One of the means adapted to improve sound quality of an audio device is an insulator. In the analog era, in order to suppress howling, the insulator was mainly placed between an analog player and a floor surface, and indispensable as a means adapted to block vibration from transferring. After the transition from the analog player to the CD player, the insulator has been used not as a measure to prevent the howling but as a tuning means adapted to improve sound quality of an audio device or make an adjustment to obtain the listener's favorite sound. It is well known that by applying an insulator, sound quality is changed; however, it cannot be said that a mechanism that brings the effect of the change in sound quality is not sufficiently theoretically elucidated, and many of the insulators are developed in an empirical or trial-and-error manner. Materials that have been used as an insulator in the past include the following two types.
(1) Floating Type Insulator
This type of insulator is intended to block (shut out) vibration, and as the insulator, a buffer having small stiffness is used. As the buffer, there is one using a rubber material, one using a spring coil, an air floating board that seals air therein, one using repulsive force based on magnetic force, or the like.
(2) Insulator Using Hard Material
Another type of insulator is one using a hard material. In recent years, in place of the above-described buffer, one using a hard material intended to effectively absorb vibration generated by an audio device to release the vibration outside, such as wood, resin, metal, or ceramic, or a composite type in which such materials are formed into a multilayered structure has been devised and commercialized. The composite type is disclosed in JPA H10-246284 (Patent literature 3). The hard insulator is used as a reproduced sound tuning means using characteristics of a good quality acoustic material. For example,
(i) Metal Materials
    Brass: Bright and brilliant sound    Copper: Heavy and powerful    Silver: Good passage of core, and quick attack/decay of sound    Gold: Rich and fascinating(ii) Wood Materials    African ebony: Hard but not stimulus sound (used for music instruments)    Macassar ebony: Softer than African ebony    Cherry: Soft and mellow
On the other hand, a cone-shaped spike is one that utilizes an effect of easily transferring vibration in a direction of “column→cone→apex of cone→floor surface” but not easily transferring it in a direction opposite to the above direction, and is frequently used for placement of a speaker. For example, a structure in which a plurality of spikes are arranged in series is disclosed in Japanese patent No. 3848987 (Patent literature 1).
A vibration-preventing support apparatus having double spike structure illustrated in FIG. 52 is configured to include: a spike support 980; a first spike 981; a second spike 982; and liquid 983 filled in the spike support 980. The first spike 981 is inserted down to a lower end of the spike support 980 such that a columnar part thereof comes into contact with an inner wall of a cylinder of the spike support 980. The second spike 982 is also inserted such that an apex of a conical part thereof is placed in a depression provided in the center of an upper surface of the first spike 981. The liquid 983 filled in a narrow gap between the spike support 980 and the first spike 981 has an effect of insulating vibration between the both members 981 and 980.